This application claims the priority benefit of Taiwan application serial no. 87100542, filed Jan. 16, 1998, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
This invention relates to digital audio signal processing techniques, and more particularly, to an apparatus and method for concealment of any erroneous part of received compressed audio data during the decompression process.
2. Description of Related Art
Large volumes of digital data, such as audio data, are usually compressed before being put into storage or transmission so as to reduce the required storage space or transmission burden. Compressed audio data should undergo a decompression process before they can be actually utilized for broadcast. During the transmission, however, errors can occur due to noises or any forms of distortions in the transmission path. When errors occur, an error detection and correction process should be performed so as to discover and resolve the errors in the received data. If the errors in the compressed audio data are not corrected, they can cause, after being decompressed for broadcast, an undesired sharp, noisy sound when being broadcast through a loudspeaker.
There exists, therefore, a need for an apparatus and method that can resolve the foregoing problem so as to allow the compressed audio data to be broadcast with their original sound quality.
It is therefore an objective of the present invention to provide an apparatus and method for error concealment of compressed audio data, which can conceal the erroneous part, if found, of the received compressed audio data so as to allow the compressed audio data to be broadcast with their original sound quality.
It is another an objective of the present invention to provide an apparatus and method for error concealment of compressed audio data, which can detect errors in the received compressed audio data and conceal them.
In accordance with the foregoing and other objectives of the present invention, an apparatus and method for error concealment of compressed audio data is provided.
The apparatus of the invention includes a packet-unit controller, a threshold controller, a scale detector, and an error-correction circuit, wherein the packet-unit controller is coupled to receive the compressed audio data, for performing an error checking and decompression operation on the compressed audio data.
The threshold controller in the apparatus according to the invention is coupled to said threshold controller, capable of generating a threshold control signal in response to the result of the error-checking operation performed by said packet-unit controller.
The scale detector in the apparatus according to the invention is coupled to receive the input compressed audio data and the output threshold control signal from said threshold controller, capable of performing a scale checking operation to check the packet length of the received compressed audio data and also to check whether any pair of successive scales in the received compressed audio data is incorrect to thereby generate and transfer a scale error signal to said packet-unit controller and said error-correction circuit.
The error-correction circuit in the apparatus according to the invention is coupled to said scale detector and said packet-unit controller, capable of performing an error concealment operation on the output decompressed audio data from said packet-unit controller based on the value of the scale error signal from said scale detector so as to discard the erroneous decompressed audio data and then output a corrected version of the discarded -data.
The method of the invention starts with decompressing the input compressed audio data followed by checking whether any pair of successive scales in the input compressed audio data is correct in ratio and whether the packet length of the input compressed audio data is correct. If either of the scale ratio or the packet length is detected to be incorrect, then performing the following substeps of discarding the current decompressed audio data, setting the threshold control signal to an error mode threshold value and detecting the number of correctly received packets. In the other hand, if the scale ratio, the packet length, and the total number of correctly received packets are detected to be correct, then performing the following substeps of outputting the decompressed audio data and then setting the threshold control signal to a normal mode threshold value.